Antenna system



Mqgh 25,'1947. P. SCARTER 2,417,808 v *ANTENNA SYSTEM Pon/EP Gw//v March25, 1947. P. s. CARTER 2,417,808

I ANTENNA SYSTEM Filed' June :50,l 1942 5 sheets-sneer 2 AT'TORNEYvMarch 25, 1947. P. s.I CARTER ANTENNA SYSTEM 1942 I5 Sheets-Sheet 3Filed June 30 Y Y. .Y Y,

. INVENTOR sie/'v- ATTORNEY Patented Mar. 25, '1947 UNITED STATES PATENTFFICEk ANTENNA SYSTEM Philip S. Carter, Rocky Point, N. Y., assignor toRadio Corporation of America, a corporation of Delaware 12 Claims.

The present invention relates to antenna systems and, more particularly,to ultra short wave directive antenna arrays.

An object of the present invention is the provision of an antenna arrayfor use onairplanes.

Another object of the present invention is the provision of an ultrashort wave antenna array to be used on airplanes for direction finding.

Still another object of the present invention is the provision of anantenna array for detecting the direction of arrival of ultra short waveradio impulses.

A further object is the provision of an antenna array for radiatingpulses of ultra short wave radio energy in a sharply directive beam, andfor receiving said pulses as they return from a, refleeting object.

A further object of the present invention is the provision of amulti-unit antenna array, in which impedance changes in the antennaarray have substantially no effect on the directivity pattern of theantenna.

Still a further object of the present invention is the provision of anantenna array which is compact in size, so that it does not adverselyaffect the aerodynamics of a plane on which it may be mounted, which ismechanically sturdy, so that it will be unaffected by the conditionsunder which it is to be used, and which is, furthermore, adapted to beconveniently mounted on an airplane.

The foregoing objects, and others which may appear from the followingdetailed description, are attained in accordance with the principles ofthe present invention, by providing a multitiered antenna, each tiercomprising one or more energized radiators and parasitic directors andreectors aligned along a desired line of directivity. The radiators aremounted perpendicular to a conductive sheet, which may be the side wallof the fuselage or body of an airplane, one on each side of the planeand near the front of the plane. Thus arranged, each antenna has itsdirection of maximum response vdirected about 12 away from dead ahead onthe plane.

The antennas are so arranged that the directivity directly ahead of theplane at a point when patterns cross the signal strength is down about1.5 decibels from the maximum response. It is contemplated thatstructure may be provided for alternately connecting first one, and thenthe other antenna, to a transmitter and receiver. Equal amplitude outputpulses from the receiver then indicate that the plane is travellingdirectly toward the signal source, thus providing a homing indication.Furthermore, the antennas may be used for transmitting pulses which,when reected from a conductive object, are received by the same antennasand are applied to a receiver as mentioned above and thus indicate itsdistance and'its direction from the plane.

The present invention will be more fully understood by reference to thefollowing detailed vdescription, which is accompanied by a drawing inwhich Figure l illustrates diagrammatically, for the purpose ofexplaining the principles of the present invention, an end re antennautilizing an energized radiator and parasitic reflector and directorradiator, and Figure 2 is a family of curves representing the eiiect `onthe directivity of the antenna, of a variation in the number `of unitsof the antenna of Figure 1 and their spacing; while Figure 3 illustratesa side View of an embodiment of the present invention shown in Figure 1;and Figure 4 is a curve showing the directivity pattern of the antennaof Figure 3; Figures 5 and 6 are plan and elevational views of Vamodification of the form of the invention shown in Figure 3,particularly designed for use on airplanes; Figures 7 and 8 illustratean enlarged cross-sectional view of the details of construction of twomodifications of the energized radiator elements of the antenna ofFigures 5 and 6; and Figure 9 is a side view of a further modificationof the invention.

In Figure 1 I have shown a vmulti-unit end re directive antenna,including an energized radiator Ill, parasitic directive radiators I2,I4, I6 and I3, and a parasitic reflector radiator 20. The antenna I0 inthis embodiment is shown as a folded half wave dipole. The foldedconstruction is used so that an impedance match between the two-wiretransmission line 9 and radiator l0 is obtained. This form ofconstruction has been fully described in my -prior application No. 155,-385, iiled July 24, 1937, now Patent #2,283,914, granted May 26, 1942,to which reference may be had f-or a more detailed description as to thetheory of operation.

The antenna of Figure 1 has a directivity pattern having a decidedmaximum of response along a common axis normal to each of the radiatorsI0, I2, I4, I6, I8 and 20. The effect on the directivity pattern of avariation in the number of radiator elements and their spacing is shownin Figure 2. For example, curve 25 of Figure 2 shows the directivity ina plane normal to the plane of the radiators of an antenna such as shownin Figure 1, comprising six radiator units, that is, one energizeddipole, one reflector dipole and four director dipoles. The spacingbetween the various elements is as shown in Figure 1. Now, if theantenna is as constructed in Figure 1, except that all units are spacedapart a distance equal to one-quarter of the operating wavelength, adirectivity pattern is obtained, as shown by curve 26. It will be notedthat a considerable drop in the power gain along the axis of the antennais encountered. If a ve-unit antenna is used, that is, one energizeddipole, one reflector and three directors, having relative spacings of.2, .4, .3, .3 wavelength, a directivity pattern is obtained as shown bycurve 2l of Figure 2. It will be noted that this directivity is somewhatbetter than that obtained by the use of a six-unit antenna, with allspacings equal, though it is less than the optimum obtainable with asix-unit antenna. Curve 28 shows the directivity obtained by a singledipole infront of a reflective sheet and may be used for comparisonsince all curves in Figure 2 have been drawn to their correct 'relativevalues.

The embodiment of my invention shown in Figure 3 utilizes quarter-waveradiators 30, 32, 34, 36, 38 and 40, mounted on a conductive sheet 29,which extends at least three wavelengths beyond radiator 38 in theforward direction, and 2.82 wavelengths in a rearward direction behindradiator 40. The radiator 30 is in this modification energized at oneend by coaxial transmission line TL. This manner of energization ispossible where quarter-wave radiators are used, since the base impedanceof a quarter-wave radiator may be made substantially equal to thecharacteristic impedance oi transmission line TL. It should beunderstood that the transducer means, such as a transmitter or receiver,may besubstituted for line TL, or connected to the other end of line TLas desired.

Director radiators 32, 34, 36 and 38, and the reector radiator 40,perform thesame functions as their corresponding elements in Figure 1..An array oftwo antennas such as shown in Figure 3, spaced apart adistance equal to .7 wavelength, results in a directivity in a planeparallel to the planes of the antennas, such as shown by curve 4 2 ofFigure 4. It will be noted that the maximum of this radiation patterndoes not occur along the axis of the antenna, but is displaced therefroma matter of 18 or so. This effect is obtained because of the limitedextent of conducting sheet 29 in front of the first director 33. Ifconducting sheet 29 were infinite in extent, of course,the maximum wouldoccur along the axis of the antenna. However, this deflection of themaximum is highly desirable when a pair of antennas is used for homingpurposes.

As amatter of interest, it may be noted that the equivalent gainobtained by a single dipole and sheet reflector antenna would fall atabout 2O on the vertical sc ale of Figure 4 which may be compared withthe maximum gain of over 60 for the antenna of Figure 3.

Figure is a plan View of a modification of Figure 3, which because ofstructural modifications is particularly designed for use on airplanes.It will be apparent that since each of the director radiators 32, 34, 35and 38, as well as the reflectorgradiator 45, are streamlined in form,as little aerodynamic disturbance as possible is created. The energizedradiator 38 shown here in end View, will be further describedwithreference to Figures 'l and 8.

The tier of radiators so far described is duplicatedbya second tierexactly similarrto the ones just described and given the saine referencenumerals primed. The second tier is spaced from the first a distanceequal to .7 wavelength. Each tier of radiators is securely mounted, asby silver soldering or welding to a mounting strip 45, which may beprovided with suitable bolt holes for attaching the array to the sidewall of an airplane fuselage.

The two tiers of the antenna are energized from a single coaxialtransmission line TL, through a pair of branch circuits 5l and 52, eachhaving an electrical length equal to an odd multiple, including unity,of a quarter of a wavelength. With tier spacings of .7 wavelength,

3A wavelength branch circuits may conveniently be used. The quarterWavelength distance is very n importannsince it results in the currentsin radiator 30 and 39 being of correct amplitude and phase, regardlessof any possible changes of irnpedance of any of the radiators of eitherof the two tiers. The current amplitudes in radiators B and 35 aredetermined solely by the impedance of line sections 5l and 52. Thereasons for this have been more fully described in my copendingapplication #445,560, led June 3, 194,2.

The elevation of the antenna shown in Figure 6 indicates the relativelengths of radiators and their spacing which I have found to result inthe most desirable directivity pattern. It will be noted that each ofthe director radiators are shorter than the energized radiator, andbecome progressively shorter with increasing distance from the energizedradiator while at the same time their spacing increases. The reflectorradiator llt is somewhat longer than the energized radiator, and isquite closely spaced therefrom. A spacing of .13 wavelength has beenfound satisfactory.

In Figures 7 and 8 are shown two modifications of energized radiator lilof Figures 5 and 6. The modification shown in Figure 7 is so designedthat the transmission line may lie on the same side of the conductingsheet as that to which the radiators are attached. The antenna isattached to the conducting sheet or supporting strip by means of amounting flange 50 carrying thereon an extending tube portion 54 withinwhich the radiator 3i) is maintained in position by insulating sleeve55. Inner conductor 5G of transmission line 5i is connected to the innerend of radiator 30. The outer sheath 51 of the transmission line 5i isconductively connected to tubular portion 54 by silver soldering orbrazing it thereto. Means are provided in the structure so that both theeffective length of the antenna and the effective position of feed onthe antenna may be adjusted so as to present the desired impedance tothe transmission line. The eifective length is changed by moving thesliding tube 58 while the effective feed point is shifted by sliding thetube 59 along the tube 54. The insulation material 55 also has a veryconsiderable effect on the impedance presented b`y the antenna. Thedimension of 0105A shown in the gure for the distance from base to endof tubel and the dimension 020.23% to the outer end of theradiator wereboth found experimentally to result in a perfect match of the maintransmission line at the junction. Under such acondition the impedancepresented by the antenna at its base is 25 ohms. This value istransformed bythe 3%; wavelength branch transmission line having a surgeimpedance of approximately 50 ohms to a value of 100 ohms at thejunction. The total value of impedance for the two.branch lines inparallel then becomes 50 4ohms at the'junction and perfectly matches themain line.

The proper dimensions having been determined by means of the structureshown in Figure '7, in the final installation of the antenna on theplane, the form of construction shown in Figure 8 may be more desirable.Here the transmission line 5 l is arranged to lie within the body of theplane, and conductors 56 and 5i thereof are connected to tube 5t andradiator 3d in coaxial alignment. The projecting length of tube 5d,together with insulation material 55, is such as to obtain an impedanceof ohms pure resistance at the base of radiator 3d. The FAA transmissionline 5l havlng a characteristic impedance of 50 ohms transforms this to100 ohms at the junction of the two lines 5i and 52. The two branchlines in parallel then present an impedance of 50 ohms to the main lineTL, thus matching the same. In this arrangement the effective length ofthe antenna is adjusted by sliding the complete unit in or out throughange 5i). This type of antenna is very sensitive to overall length butrelatively insensitive to moderate changes in the position of theeffective feed point. The impedance presented depends, in addition tothe effective length of the antenna, considerably upon the length of theinsulation material extended along the exposed portion. The dimensionsshown in the figure were arrived at experimentally and resulted in aperfect match at the transmission line junction. The adjustment may bemaintained by owing solder between ange Sil and tube 59.

The further modifi-:ation of the present invention shown in Figure 9constitutes a nineelernent antenna. This particular form of constructionis desirable where a large number of radiating elee ments must lbe used,since it has been discovered that Where more than five parasiticelements are used with a single energized element the currents in themost remote elements are relatively low so that the optimum gain is notobtained. Therefore, two elements are energized, while the remainderareparasitic. With two or more energized radiator elements, it is desirablethat they be arranged to be energized in an in-phase relationship, sincethis relationship may be more conveniently maintained than anyfractional relationship. The two directly energized units et and 'i0 areso arranged that they are exactly a wavelength apart. They are energizedin the same phase through branch coaxial lines Eil and li, havinglengths equal to an odd multiple of a quarter wavelength. Thus, theamplitude and phase relationships of currents in radiators 5G and iiiare not affected by the dimensions of the radiators themselves, but onlyby the constants of lines 6l and li, respectively. The currents mustthus always remain in the correct amplitude and phase relationship,regardless of any see-sawing of the impedance, such as may be caused byice deposits on the radiators themselves, or by undesired mutualimpedance effects from the associated reectors and directors. Threeparasitic director radiators l2, 'l and 16, and one parasitic reflectorradiator lg, obtain most of their excitation from radiator lil, whileenergized radiator El) supplies energy to parasitic director 62 and 65and parasitic reiiector radiator 56.

The conducting sheet B9 has the same function as conducting sheet 2S ofFigure 3, and its dimensions at each end of the array should be of thesame magnitude as they are in Figure 3, in order that the directivitypattern win have its maximum in the proper direction.

While the foregoing detailed description has been predicated, forconvenience, upon the assumption that the antenna is to be used for theradiation of short wave energy, it is to be understood that the antennamay equally well be employed for the reception of Shortwave energy orfor both in alternation.

Furthermore, while I have particularly shown and described severalmodifications of the present invention, it should be clearly understoodthat the invention is not limited to these forms alone, but thatmodications may be made.

claim:

1. A directive antenna array including an energized antenna coupled to ahigh frequency transducer means, a plurality of parasitic directorantennas and a parasitic reflector antenna, all or" said antennas beingarranged perpendicularly to a common axis of directivity and in a singleplane, the spacing of said director antennas varying directly and theirlengths varying inversely as their distance from said energized antenna.

2. A directive antenna array including an eri-- ergized antenna coupledto a high frequency means, a plurality of parasitic director antennasand a parasitic reflector antenna, all of said antennas being arrangedperpendicular to a conimon conducting sheet and along a common line ofdirectivity on said sheet, the spacing of said director antennas varyingdirectly and their length varying inversely as their distance from saidenergized antenna.

3. An antenna system including a plurality of arrays, as set forth inclaim 1, said arrays being arranged in parallel planes and spaced aparta distance substantially equal to .'7 wavelengths and each of saidenergized antennas being coupled to said transducer means through equallength transmission line sections.

4:. A directive antenna array including an energized antenna coupled toa high frequency means, a plurality of parasitic director antennas and aparasitic reflector antenna, all of said antennas being arrangedperpendicular to a common conducting sheet and along a common line ofdirectivity on said sheet, the spacing of said director antennas varyingdirectly and their length varying inversely as their distance from saidenergized antenna, the said conducting sheet extending beyond saidantennas along said line of directivity a distance such that a radiationmaximum takes place at an angle to the plane of said sheet of from l0 to20 degrees.

5. A directive antenna array including an energized antenna coupled to ahigh frequency transducer means, a plurality of parasitic director'antennas and a parasitic reflector antenna, all of said antennas beingarranged perpendicular to a common axis of directivity and in a singleplane, the spacing of said director antennas varying directly and theirlengths varying inversely as their distance from said energized antenna,the spacing of said reflector antenna from said energized antenna beingof the order of oneeighth of the operating wavelength and its lengthsubstantially equal to the length of said energized antenna.

6. A directive antenna array including an energized antenna coupled tohigh frequency transducer means, a plurality of parasitic directorantennas and a parasitic reflector antenna, all of said antennas beingarranged perpendicular to a common conducting sheet and along a commonline of directlvity on said sheet, the spacing o! said director antennasvarying directly and their length varying inversely as their distancefrom said energized antenna, the spacing of said reflector antenna fromsaid energized antenna being of the order of one-eighth of an operatingwavelength and its length substantially equal to said energized antenna.Y

7. An antenna system including a plurality of arrays, as set forth inclaim 6, said arrays being arranged in parallel planes spaced apart adistance substantially equal to .'7 wavelengths and each of saidenergized antennas being coupled to said transducer means through equallength transmission line sections, said transmission line sectionshaving lengths equal to an odd multiple, including unity, of a quarterWavelength.

8. In a directive antenna array including a plurality of radiatorsarranged along a. desired line of directivity, some of said radiatorsbeing connected to a source of high frequency energy and others adaptedto be parasitically energized from said energized radiators, saidconnected radiators being so spaced that they may be energized in an inphase relationship, and equal length transmission lines for connectingsaid energized radiators to said source of high frequency energy, eachhaving a length equal to an odd multiple of a quarter of the operatingwavelength whereby the current in each of said energized radiators isindependent of the impedance of said radiators.

9. A directive antenna system including a plurality of radiatorsarranged one behind another along a desired line of directivity, some ofsaid radiators being connected to transducer means by equal lengthtransmission lines whereby the energy in said connected radiators is inan inphase relationship, said connected radiators being spaced apart adistance equal to the operating wavelength, the lengths of saidtransmission lines being equal to an odd multiple including unity of onequarter of the operating wavelength whereby the relative currents insaid connected radiators are determined solely by the relative 2,292,791

impedances of the transmission lines.

10. An antenna array including a plurality of radiators connected to a,source of high frequency energy, said radiators being so spaced thatthey may be energized in an inphase relationship, and equal lengthtransmission lines for connecting said radiators to said source of highfrequency energy, the length of said transmission lines being equal toan odd multiple, including unity of one quarter of the operatingwavelength whereby the current in each of said radiators is independentyof the impedance of said radiators.

11. A directive antenna system including a plurality of parallelantennas lying in a plane perpendicular t0 a conductive sheet and soarranged that the direction of maximum response of said system liesalong said plane, said conductive sheet extending beyond said antennasin the direction of maximum response of said system a distance such thatthe direction of maximum response along said plane is elevated withrespect to said conductive sheet.

12. A directive antenna array including an energized antenna coupled toa high frequency means, a plurality of parasitic director antennas and aparasitic reflector antenna, all of said antennas being arrangedperpendicular to a common conducting sheet and along a common line ofdirectivity on said sheet, said director antenas being shorter than saidenergized antennas, the said conducting sheet extending beyond saidantennas along said line of directivity a distance such that a radiationmaximum takes place at an angle to the plane of said sheet of from 10 to20 degrees.

PHILIP S. CARTER.

REFERENCES CITED The following references are of record in the lle ofthis patent:

UNITED STATES PATENTS Number Name Date 1,740,851 Franklin Dec. 24, 19291,745,342 Yagi Jan. 28, 1930 Mins Aug. 11, 1942 1,643,323 Stone Sept.27, 1927

